A plasma display panel (hereinafter abbreviated as “panel”) is one of well-known image display devices having a large number of pixels arranged two-dimensionally. The panel includes a large number of discharge cells having scan electrodes, sustain electrodes, and data electrodes. In each discharge cell, a gas discharge is generated to excite and illuminate phosphors, thereby achieving color display.
A plasma display device with such a panel displays image mainly uses a subfield method. This method divides one field into a plurality of subfields having predetermined luminance weights, and each discharge cell is controlled to emit or not to emit light in each subfield so as to display image.
A plasma display device includes a scan electrode drive circuit for driving scan electrodes, a sustain electrode drive circuit for driving sustain electrodes, and a data electrode drive circuit for driving data electrodes. These driving circuits apply the electrodes with necessary drive voltage waveforms. The data electrode drive circuit is generally composed of dedicated ICs because it needs to apply address pulses required for an address operation individually to the large number of data electrodes based on an image signal. When the panel is viewed from the perspective of the data electrode drive circuit, each data electrode is a capacitive load with stray capacitance between itself and adjacent data electrodes and between itself and the corresponding pair of scan electrode and sustain electrode. Therefore, in order to apply the data electrodes with drive voltage waveforms, the capacitance has to be charged and discharged, thereby consuming electric power. The data electrode drive circuit, however, requires minimizing its electric power consumption in order to be integrated into an IC.
The electric power consumption of the data electrode drive circuit increases as the current to charge and discharge the capacitance of the data electrodes increases. The charge-discharge current largely depends on the image signal representing the image to be displayed. For example, when address pulses are not applied to any of the data electrodes, the charge-discharge current becomes “0”, and hence, the data electrode drive circuit requires minimum electric power. When address pulses are applied to all data electrodes, on the other hand, the charge-discharge current also becomes “0”, and hence, the data electrode drive circuit requires low electric power. When address pulses are applied in a random order to the data electrodes, however, the charge-discharge current is large. In particular, when address pulses are applied alternately to adjacent data electrodes, the data electrode drive circuit consumes large electric power. This is because the data electrode drive circuit needs to charge and discharge the capacitance between adjacent data electrodes and the capacitance between a data electrode and the corresponding pair of scan electrode and sustain electrode.
A proposed method for reducing the electric power consumption of the data electrode drive circuit is as follows (see, for example, Patent Document 1). The electric power consumption of the data electrode drive circuit is predicted based on an image signal, and the address operation in subfields is inhibited in ascending order of luminance weight.
Another proposed method for reducing the electric power consumption of the data electrode drive circuit is as follows (see, for example, Patent Document 2). Instead of completely inhibiting the address operation in subfields, the frequency of an address operation is reduced. This method can maintain image display quality although the effect of reducing the electric power is smaller than the method of Patent Document 1.
Another proposed method for reducing the electric power consumption of the data electrode drive circuit is as follows (see, for example, Patent Document 3). The charge-discharge current is reduced by changing the order in which to apply address pulses to the data electrodes. This method can maintain image display quality although the effect of reducing the electric power largely depends on the image to be displayed.
In recent years, along with the increasing definition and screen size of the panels, the data electrode drive circuit requires an increasing amount of electric power. As described above, however, in order to integrate the data electrode drive circuit into an IC, it is impossible to increase its electric power without limitation. It is also impermissible to greatly reduce image display quality because high image quality is essential. When some methods for processing image signals are switched in order to reduce the electric power consumption of the data electrode drive circuit, it is impermissible to cause a decrease in image display quality such as flickering due to the switching.
Patent Document 1: Japanese Patent Unexamined Publication No. 2000-66638
Patent Document 2: Japanese Patent Unexamined Publication No. 2002-149109
Patent Document 3: Japanese Patent Unexamined Publication No. H11-282398